Let's try to think how it interacts with the current noteOn() and noteGrainOn() API. For example, what if we want to play a grain backwards. Then it will have to start playing back at the end of the grain. Let's try to make sure we get the API correct before implementing a quick fix. I think it will be useful, but let's do it right.

(In reply to comment #2)
> Let's try to think how it interacts with the current noteOn() and noteGrainOn() API. For example, what if we want to play a grain backwards. Then it will have to start playing back at the end of the grain. Let's try to make sure we get the API correct before implementing a quick fix. I think it will be useful, but let's do it right.
That would be what I would want and expect with noteGrainOn() and a negative playbackRate: play just the selected grain backwards.